CO2 sequestration by pH-swing mineral carbonation based on HCl/NH4OH system using iron-rich lizardite 1T

In pH-swing mineral carbonation, several acid/base systems has been investigated. Currently the main acid/base systems employed are HCl/NaOH and NH4HSO4/NH4OH. However, the use of a HCl/NH4OH system was not yet elucidated. This study proposes to evaluate the feasibility of a pH-swing mineral carbonation based on HCl/NH4OH system at atmospheric pressure and moderate temperatures using mining waste from asbestos production from Goias State, Brazil (S-GO) for two conditions (i.e. stoichiometric conditions (T2E) and acid excess (T2)). Results indicated that the Fe3+ content in S-GO acted as a catalyst, due to FeCl3 hydrolysis in aqueous solutions. Thus, high Mg and Fe extraction efficiency (95 +/- 2%), were achieved in the leaching stage for both conditions. The Si solid residue was mainly SiO2 with 90 +/- 1% purity content. In the purification stage 91.7 +/- 1.9% of Fe, were removed, however, a loss of Mg of 13.6 +/- 2.3% was also detected. On the carbonation stage, high purity hydromagnesite was formed in T2E; this stage had a 85% efficiency, thus, 36.7% of CO2 was fixed. On T2, excess H2O and CO2 promoted dypingite formation and reduced hydromagnesite formation. After carbonation, the formation of crystals was observed in the NH4Cl aqueous solution at 25 degrees C, indicating NH4Cl supersaturation. The results of mass balance indicate that 4 ton of mineral waste will be employed for each ton of captured CO2, as well as 2.6 ton of HCl, and 4.5 ton of NH4OH. However, 1.7 ton of SiO2, 0.55 ton of iron oxides, and 2.7 ton of hydromagnesite could be produced.